Tested: vortex generators (AirTabs) on a Toyota Corolla

[mobilerik]

Hey Metro - I couldn't tell from the pics or description if you used the commercial version of Air-tabs, or if they were your own DIY version.

I made my own out of flashing that are very similar to the commercial ones (as far as I can tell, as I haven't actually seen one in person) but I think they're taller, probably too tall. I mounted them on the top so far, 8 across, 6 in. center spacing.

I agree about the noise - that was the first thing I noticed. But for all the noise, I don't notice any added drag. On my regular commute, my DWL holding mpg has been about the same, maybe slightly better holding times, but it's hard to tell. My numbers are up about 1mpg, but that could just as well be my car adjusting to my belly screen install (which was huge, as I expected, since the PreRunner comes lifted).

I want to cut them down a bit, I think, and I want to add them on the sides and belly, too, but I'd like to find a way to make them look better... maybe transparent.

[Cd]

" you can end up with a net increase in drag (or zero sum gain), even while you apparently improve downstream flow."

Thanks Metro ! I learned something new today !

I had thought for sure that by seeing a smoother flow, that this meant a reduction in drag .

[MetroMPG]

Cd, the key word was "apparently".

The tufts may have been streaming back better with the VG's in place, but I have no idea what's actually going on above the glass. A smoke test would reveal more.

Originally Posted by akashic

Hey Metro - I couldn't tell from the pics or description if you used the commercial version of Air-tabs, or if they were your own DIY version.

They're the commercial ones.

I agree about the noise - that was the first thing I noticed. But for all the noise, I don't notice any added drag.

I believe wind noise = drag.

On my regular commute, my DWL holding mpg has been about the same, maybe slightly better holding times, but it's hard to tell.

A-B-A is your friend. All else is madness!

[mobilerik]

Originally Posted by MetroMPG

I believe wind noise = drag.

I was hoping that was the sound of tornado-like vortices lifting my mpgs into the stratosphere.

Besides, if I strapped a jet engine on top of my truck, that might be a little "noisy" too, doncha-think?

Originally Posted by MetroMPG

A-B-A is your friend. All else is madness!

In other words, if you're not a Swedish superpop sensation, you must be a nutty British ska band.

Or is that not what you're saying...?

[bwilson4web]

Note from admin: copied this post and the next one from this thread: http://ecomodder.com/forum/showthrea...html#post97726

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Originally Posted by MetroMPG

My opinion, based on as-controlled-as-possible A-B-A testing (straight & level road, absent any other traffic, cruise controlled, back to back bi-directional runs) is you'll not likely see any drag reduction using AirTabs. Seen this? http://ecomodder.com/forum/showthrea...olla-2390.html. . . .

Thanks! A few questions:

1. How much warm-up time and speed before the first "A" test? (Prius warm-up is ~30 min., thermal changes takes about 5-10 minutes.)
2. How much warm-up time before the first "B" test?
3. How much warm-up time before the second "A" test?
4. How many minutes per run?
5. Ambient temperature that day?
6. Start and stop times?

My hypothesis is driving to the test area may have been long enough to warm-up the vehicle. Entering the first "A" protocol would have 'good data.' Then adding the vortex generators would allow the vehicle to 'cool off' somewhat. Then taking off the vortex generators for the second "A" appears to be much closer to the "B". I think I'm seeing the pattern in a plot of the data.

What has peaked my interest in the protocol is the second "A", especially the "West" runs really look different. The "East" runs are more consistent ... given the limited number of runs.

Are the vortex generators still available?

I am thinking about replicating the test using 104 kph (65 mph) that corresponds to the last plateau before MPG drops off.

Thanks,
Bob Wilson

[MetroMPG]

Originally Posted by bwilson4web

Thanks! A few questions:

1. How much warm-up time and speed before the first "A" test? (Prius warm-up is ~30 min., thermal changes takes about 5-10 minutes.)

The day of the test, the max temp was 18C - I didn't record the actual early evening temp when I ran the test. It takes me 20-25 minutes to get to the test route (combination of sub/urban and rural driving). The car may also have already been warm prior to setting out (didn't make a note of that).

How much warm-up time before the first "B" test?

The airtabs were attached with tape in approximately 2 minutes. The engine was left on during this.

How much warm-up time before the second "A" test?

It would have taken less than a minute to remove the tabs, engine left running again.

How many minutes per run?

1.6 km at 90 km/h for the run itself (~64 sec), plus time getting up to speed, plus time coasting to a stop, jotting down the run data & turning the car around. 2-3 minutes per run is probably a good guess.

Are the vortex generators still available?

Yes. I can send them to you if you like. PM me your mailing address.

[evolutionmovement]

If you don't mind me asking, how much were the VGs? I'm thinking they might be worth trying when I get my wagon back on the road.

[MetroMPG]

I'll say again: I don't think they're worth trying. I also tested them on a minivan (approximates the shape of a hatchback or wagon), A-B-A approach. No discernable effect. See: http://ecomodder.com/forum/showthrea...fect-6381.html

I was given these by a distributor. I think they cost $2.50 each new.

[The Rooster]

Before I get started...I'm an aero-nub, so go easy on me.

Is the drag created by the VG's more a function of the frontal area, which was determined to be about as much as a small mirror, or the acutal areodynamic effect caused by them?

If it's the former, then I wonder why not consider a VG with virtually no frontal area. When I was an AV-8B Harrier mechanic, the VG's on the wings of those aircraft were esentially aluminum tabs bent at 90 degrees and riveted to the wings at what appeared to be, by eye, parallel to the direction of forward flight. When we broke them off, which happens when you climb on the wings from time to time, the Airframes shop would simply bend up a new one out of scrap aircraft aluminum and re rivet them back on. I imagine for testing, double backed tape should work, though the tape would have more frontal area than the tab itself.

Here's a link to a photo of a Harrier wing where you can see the arangement, size and spacing of the VG's on the wing. If it matters, the harrier is sub-sonic so any aerodynamic design of the aircraft wouldn't/didn't include sonic compresion...or whatever you call the sonic boom, so the VG design isn't compensating for anything super-sonic;



The VG's on those things are rather small, something like 1.5" long by maybe 3/4" of an inch tall...I'm trying to remember, but it was a decade ago.

Anyway, that was all a long winded way of asking if the drag is caused by frontal area, or the generated vortex following the VG's.

[MetroMPG]

Hi Rooster - if I were trying to fix an aerodynamic problem, I'd definitely use the VG's like the ones you show, or the "delta" style VG's that Mitsubishi used on the EVO. For the reasons stated.

That said, let's remember: the famous Mitsu paper showed only an infinitesimally small Cd improvement even when its delta VG's placement & size were optimized through computational fluid dynamics.